The invention had the object of finding novel compounds having valuable properties, in particular those which can be used for the preparation of medicaments.
The present invention relates to compounds and to the use of compounds in which the inhibition, regulation and/or modulation of signal transduction by kinases, in particular tyrosine kinases, furthermore to pharmaceutical compositions which comprise these compounds, and to the use of the compounds for the treatment of kinase-induced diseases.
Because protein kinases regulate nearly every cellular process, including metabolism, cell proliferation, cell differentiation, and cell survival, they are attractive targets for therapeutic intervention for various disease states. For example, cell-cycle control and angiogenesis, in which protein kinases play a pivotal role are cellular processes associated with numerous disease conditions such as but not limited to cancer, inflammatory diseases, abnormal angiogenesis and diseases related thereto, atherosclerosis, macular degeneration, diabetes, obesity, and pain.
One of the key events in the signaling pathway following the activation of mast cells is activation of the tyrosine kinase Syk. Mast cells play a critical role in asthma and allergic disorders by releasing pro-inflammatory mediators and cytokines. Antigen-mediated aggregation of FcεRJ, the high-affinity receptor for IgE, results in activation of mast cells. This triggers a series of signaling events resulting in the release of mediators, including histamine, proteases, leukotrienes and cytokines. These mediators cause increased vascular permeability, mucus production, bronchoconstriction, tissue degradation and inflammation, thus playing key roles in the etiology and symptoms of asthma and allergic disorders. Syk kinase acts as a central initiator of all subsequent signaling leading to mediator release. The critical role of Syk kinase in the signaling path was demonstrated by the complete inhibition of mediator release by a protein containing the SH2 domains of Syk kinase that functioned as an inhibitor of Syk kinase (J. A. Taylor et al, Molec. and Cell Biol, 15: 4149-4157 (1995)).
Syk (Spleen-Tyrosine-Kinase) is a 72 kDa non-receptor tyrosine kinase belonging to the subfamily of intracellular tyrosine kinases that comprises ZAP70, Pyk2, Abl, Tie2, KDR and HER, among others. Syk is a major regulator of FcR (FcγRI, II, III, FcεRI, FcαR) and BCR signaling and is expressed throughout hematopoietic lineage, as well as in fibroblasts, osteoclasts, hepatocytes, epithelial and neuronal cells. In addition to the C terminal kinase domain, SYK exhibits two SH2 domains and over 10 autophosphorylation sites1.
By means of both its SH2 domains SYK is specifically recruited to phosphorylated ITAMs (Immunoreceptor Tyrosine-based Activation Motifs present in immunoreceptors such as FcγRI, IIA, IIIA, FcαR, FcεRI and BCR, expressed by monocytes, macrophages, mast cells, neutrophils and B cells) and specifically mediates immunoreceptor signaling triggered by activation of those receptors in mast cells, B cells, macrophages, monocytes, neutrophils, eosinophils, NK cells, DC cells platelets and osteoclasts1,2.
Upon BCR cross linking, tyrosine residues at the ITAM motifs of the cytosolic tail of the Igα/Igβ are phosphorylated by the Src-family kinase Lyn, generating docking sites for SYK that is thus recruited to the BCR immunocomplex. SYK is then phosphorylated and activated by the Src-family kinase Lyn. Upon activation, SYK will phosphorylate the adaptor protein BLNK allowing its interaction with both BTK and PLCγ2 via their respective SH2 domains. SYK phosphorylated—and thus activated—BTK will in turn phosphorylate and activate PLCγ2 leading to IP3 formation, Ca2+ mobilization, PKC and MAPK activation and consequent NFAT, AP-1 and NFκB transcription factor activation, resulting in activation and surface marker expression, cytokine release, survival and proliferation of B cells3. In mast cells, allergen activated FcεRI is phosphorylated by LYN and FYN and recruits SYK which is in turn phosphorylated by LYN and further autophosphorylated, becoming fully activated. Activated SYK phosphorylates the two adaptor molecules NTAL and LAT creating more docking sites for SH2 containing proteins such as PLCγ1, vav, and the p85 regulatory subunit of PI3K, resulting in mast cell degranulation and cytokine production4. Syk's critical role in signal transduction of mast cells is confirmed by reproducible observation that the 10-15% of basophils (circulating mast cells) from human donors that cannot degranulate have reduced amounts of Syk protein5,6. In addition, SYK is required for the bone resorption activity of osteoclasts. Upon stimulation of osteoclasts by αvβ3 integrin, SYK becomes phosphorylated, most likely by c-Src, in a DAP-12/FcγRII dependent mechanism, leading to SPL-76 and Vav3 phosphorylation and subsequent cytoskeletal reorganisation. SYK deficient osteoclasts are inactive and show defective cytoskeletal reorganisation. In correlation with this, SYK deficient embryos show defective skeletal mass7,8.
BCR-mediated activation of B-cells in the lymph nodes, as well as FcR-mediated activation of dendritic cells, monocytes, macrophages, neutrophils and mast cells in the joints, are essential components of the cellular patho-physiological mechanisms taking place during rheumatoid arthritis (RA). Moreover, activation of osteoclasts leads to the bone and cartilage destruction which are hallmarks of this pathology9. SYK signaling should therefore play a pivotal role during the development of arthritis, both at the periphery and on the site of inflammation10. Indeed, an orally available Syk inhibitor R406—developed by Rigel—induced a significant improvement of clinical scores and significantly reduced serum cytokine concentrations, as well as bone erosion, in a murine model of RA11,12. Moreover, this inhibitor has shown efficacy (ACR scores improvement) and good tolerability in RA Phase II studies in humans13,14,15.
In SLE B cells contribute essentially towards pathogenesis via production of autoantibodies resulting in immune complex formation, stimulation of Fc receptors and finally in an excessive and chronic activation of inflammation. In a murine model of SLE treatment with a Syk inhibitor resulted in a reduction of numbers of class-switched germinal center, marginal zone, newly formed and follicular B cells and therefore in disease mitigating effects18.
Although TCR signals are transmitted by the intracellular tyrosine kinase ZAP-70 in thymocytes and naïve T cells, several studies indicate that differentiated effector T cells, such as those involved in the pathophysiology of Multiple sclerosis (MS) or systemic lupus erythematosus (SLE), show a down regulation of the TCRzeta chain and a concomitant upregulation of the TCR/CD3 chain and its interaction with FcRγ. Those studies show that the TCR/CD3/FcRgamma complex in effector cells recruits and activates Syk, instead of ZAP-70, tyrosine kinase. This physiologic switch in TCR signaling occurs exclusively in effector, and not naive or memory T cells16,17,18. Not surprisingly then, SYK inhibitors have been shown to delay disease progression and to improve survival in murine models of SLE17,18,19,20,21.
SYK inhibitors may also find a use in asthma, allergy, multiple sclerosis and other diseases such as thrombocytopenia purpura and T or B cell lymphomas1,10,14,22-35. Treatment of prediseased NZB/W mice with a Syk inhibitor prevented the development of renal disease demonstrated by reduced glomerular sclerosis, tubular damage, proteinuria and BUN levels18.